The present invention relates to apparatus for the measurement of the wall thickness of tubes, having measuring bodies which bear resiliently against the inner wall surface of the tube and which react upon a measuring device arranged externally of the tube wall. Such measuring devices are used in particular for the testing of the wall thickness of synthetic tubes immediately after the issue of these tubes from the nozzle of an extruder. It has been shown that during this use of the measuring device a stable support of the measuring body and an efficient protection of the same from damage is indispensable, since especially at the beginning of production substantial irregularities often occur on the inner wall surface of the tube, which can damage the measuring body bearing against the wall of the tube, or its support.